As illustrated in FIG. 41, a steering apparatus for an automobile is constructed so that the rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, and as the input shaft 3 rotates a pair of tie rods 4 are pushed or pulled and applies a steering angle to front steered wheels. The steering wheel 1 is supported by and fastened to a rear-end portion of a steering shaft 5, and the steering shaft 5 is inserted in the axial direction through a cylindrical steering column 6, and is supported by the steering column 6 so as to be able to rotate freely. Moreover, the front-end portion of the steering shaft 5 is connected to the rear-end portion of an intermediate shaft 8 by way of a universal joint 7, and the front-end portion of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9. In the illustrated example, an electric power-steering apparatus is assembled, and at a front-end portion of the steering column 6, an electric motor 10 which is an auxiliary power source that provides auxiliary power is supported by a housing 11 that is fastened to a front-end portion of the steering column 6, and an output torque (auxiliary power) from the electric motor 10 is applied to a steering shaft 5 by way of a gear unit that is provided inside the housing 11.
In this kind of steering apparatus for an automobile, a position adjustment apparatus for adjusting the height position and forward-backward position of the steering wheel according to the size or operating posture of the driver is normally assembled. In the case of the conventional construction illustrated in FIG. 41, the front-end portion of the housing 11 is supported by a vehicle body 12 by way of a tilt shaft 13 that is arranged in the width direction so as to be able to pivotally displace with respect to the vehicle body 12. The portion near the rear end of the middle portion of the steering column 6 is supported by the vehicle body 12 by way of the support bracket 14 while being held in the width direction from both sides by a pair of support-plate portions 15 that constitute a support bracket 14 that are separated in the width direction. A displacement bracket 18 is provided in the portion on the bottom surface of the portion near the rear end of the middle portion of the steering column 6 that is held by the pair of support-plate portions 15. Here, the “width direction” refers to the width direction of the vehicle body in which the steering apparatus is assembled. Further, the forward-backward direction” refers to the forward-backward direction of the vehicle body.
Long holes 23 in the up-down direction that extend in the up-down direction in an arc shape centered around the tilt shaft 13 are formed in each of the pair of support-plate portions 15. Displacement-side through holes (through holes) 27 are formed in portions of part of the displacement bracket 18 that are aligned with the part of the long holes 23 in the up-down direction. In the construction illustrated in FIG. 41, a tilt and telescopic mechanism that is capable of adjusting not only the up-down position of the steering wheel 1, but also the forward-backward position thereof, is assembled, so the displacement-side through holes 27 are long holes in the forward-backward direction that extend in the axial direction of the steering shaft 5 and steering column 6. Furthermore, the steering shaft 5 and steering column 6 are both constructed so as to be able to expand or contract. An adjustment rod 24 is inserted in the width direction through the long holes 23 in the up-down direction and the displacement-side through holes 27. Furthermore, an anchor portion (not illustrated) is provided at a base-end portion of the adjustment rod 24, and by providing an adjustment lever (not illustrated) at a tip-end portion of the adjustment rod 24, a lock mechanism is formed that expands or contracts the space between the inside surfaces of the pair of support-plate portions 15 according to the pivotal rotation of the adjustment lever. When adjusting the position of the steering wheel 1, the space between the inside surfaces of the pair of support-plate portions 15 is expanded by pivotally rotating the adjustment lever in a specified direction. In this state, the up-down position and the forward-backward position of the steering wheel 1 can be adjusted within the range that the adjustment rod is able to move inside the long holes 23 in the up-down direction and the displacement-side holes 27. After the steering wheel 1 has been moved to a desired position, the adjustment lever is pivotally rotated in the opposite direction, which contracts the space between the inside surfaces of the pair of support-plate portions 15, and the steering wheel 1 is maintained in the adjusted position.
More detailed construction of a steering wheel position adjusting apparatus is disclosed in JP 2011-121443 (A) and illustrated in FIG. 42 to FIG. 45. This steering wheel position adjusting apparatus as well has a tilt and telescopic mechanism. The steering column 6a is constructed such that the overall length thereof can be expanded or contracted by fitting the front-end portion of an outer column 16 of the rear side with the rear-end portion of an inner column 17 on the front side so that displacement in the axial direction is possible. Moreover, the front-end portion of the outer column 16 is an incomplete cylindrical shape having a diameter that can be elastically expanded or contracted. By increasing or decreasing the force by which the front-end portion of the outer column 16 is held from both sides in the width direction, it becomes possible for the inner diameter of the outer column 16 to expand or contract. The steering shaft 5a is supported on the radially inward side of the steering column 6a so as to be able to rotate freely. The steering shaft 5a is also constructed such that the overall length can be expanded or contracted by combining an outer shaft 19 and an inner shaft 20.
An electric motor 10a and housing 11a are connected and fastened to the front-end portion of the steering column 6a. The housing 11a is inserted into a support tube 21 that is provided in the width direction at the top portion, and is supported by part of the vehicle body by way of a bolt (not illustrated) that corresponds to the tilt shaft 13 so as to be able to pivotally displace. Moreover, a support bracket 14a is located at the middle portion of the steering column 6a. The support bracket 14a has an installation-plate portion 22 and a pair of support-plate portions 15a, 15b that are made of metal such as steel plate that has sufficient strength and rigidity and are connected together by welding or the like. The installation-plate portion 22 is fastened to and supported by the vehicle body 12 by way of a vehicle-side bracket (not illustrated) so as to be detachable in the forward direction due to an impact load that is applied during a secondary collision.
Moreover, long holes 23 in the up-down direction that have a partial arc shape centered around the center axis of the support tube 21 are formed in positions in the pair of support-plate portions 15a, 15b that are aligned with each other. A supported portion 26 that is constructed by a pair of supported-wall portions 25 that are separated in the width direction is provided on the top of the front portion of the outer column 16, and long holes 27 in the forward-backward direction that extend in the axial direction of the outer column 16 are formed in the pair of supported-wall portions 25. The outer column 16 is supported between the pair of support-plate portions 15a, 15b by an adjustment rod 24 that is inserted through the long holes 23 in the up-down direction and the long holes 27 in the forward-backward direction. Therefore, the outer column 16 is able to pivotally displace in the up-down direction centered around the bolt that is inserted in the support tube 21 within the range that the adjustment rod 24 is able to displace inside the long holes 23 in the up-down direction, and is able to displace in the forward-backward direction (axial direction) within the range that the adjustment rod 24 is able to displace inside the long holes 27 in the forward-backward direction.
An outward-facing flange portion 28 that corresponds to the anchor portion is provided around the base-end portion (right-end portion in FIG. 45) of the adjustment rod 24, and a cam apparatus 31 that has a drive-side cam 29 and a driven-side cam 30 is provided on the tip-end portion (left-end portion in FIG. 45) of the adjustment rod 24. By rotating and driving the drive-side cam 29 using an adjustment lever 32, the distance between the driven-side cam 30 and the flange portion 28 can be expanded or contracted. In other words, as disclosed in JP 2002-059851 (A), cam surfaces are formed on the surfaces of the drive-side cam 29 and driven-side came 30 that face each other, and these cam surfaces each has concave and convex portions that alternate continuously in the circumferential direction by way of inclined surfaces. In a state in which convex portions of each surface abut on each other, the dimension in the axial direction of the cam apparatus 31 is expanded, and in a state in which the convex portions of one surface and the concave portions of the other surface are aligned, the dimension in the axial direction of the cam apparatus 31 is contracted. The drive-side cam 29 is connected and fastened to the base-end portion of the adjustment lever 32, and the driven-side cam 30 engages in a long hole 23 in the up-down direction such that only displacement along the long hole 23 in the up-down direction is possible, or in other words, such that the rotation centered around the adjustment rod 24 is prevented.
When adjusting the position of the steering wheel 1, the adjustment lever 32 is rotated downward to cause the dimension in the axial direction of the cam apparatus 31 to contract, which causes the distance between the driven-cam 30 and the flange portion 28 to increase. As a result, the distance between the inside surfaces of the pair of support-plate portions 15a, 15b increases and the surface pressure at the contact areas between the inside surfaces of the pair of support-plate portions 15a, 15b and the outside surfaces of the pair of supported-wall portions 25 decreases or is lost. In this state, the support force of the supported portions 26 with respect to the support bracket 14a is decreased or lost, so the outer column 16 is able to displace and the position of the steering wheel 1 can be adjusted.
After the position of the steering wheel 1 has been adjusted, the adjustment lever 32 is rotated upward causing the dimension in the axial direction of the cam apparatus 31 to expand, and causing the distance between the driven-side cam 30 and the flange portion 28 to decrease. As a result, the inside surfaces of the pair of support-plate portions 15a, 15b come in strong contact with the outside surfaces of the pair of supported-wall portions 25, and the up-down position of the steering wheel 1 is fixed. At the same time, the diameter of the front-end portion of the outer column 16 where the pair of supported-wall portions 25 are provided contracts, causing the inner circumferential surface of the front-end portion of the outer column to come in strong contact with the outer circumferential surface of the rear-end portion of the inner column 17 such that the steering column 6a cannot be expanded or contracted. As a result, the forward-backward position of the steering wheel 1 is fixed.
When compared with construction that employs a screw mechanism having a nut and bolt (stud) as a tightening mechanism, a position adjustment apparatus for a steering wheel in which a cam apparatus 31 is assembled as a tightening mechanism is able to obtain a large tightening force while keeping the amount of rotation of the adjustment lever 32 small. However, in using the cam apparatus 31, when the adjustment lever 32 is rotated in a specified direction (normally downward) in order to adjust the position of the steering wheel 1, there is a possibility that the rotation of the adjustment lever 32 will be too strong. The reason for this is that when moving from a state in which the convex portions on the cam surfaces of the drive-side cam 29 and driven-side cam 30 abut on each other to a state in which the convex portions are moved toward the concave portions on the opposing surface by rotating the adjustment lever in a specified direction, the convex portions vigorously slide down the inclined surfaces of the cam surface on the opposing side. As a result, the adjustment lever 32 to which the drive-side cam 29 fastened at the base-end portion vigorously rotates in a specified direction, which may cause the driver who operates the adjustment lever to feel discomfort or unpleasant, or may cause an unpleasant collision sound to occur.
This kind of problem becomes severe when the cam apparatus is assembled in the steering wheel position adjusting apparatus as the tightening mechanism, however, even in construction that employs a screw mechanism as the tightening mechanism, there is a possibility that this problem will occur to some extent. In other words, even in the case of a tightening mechanism that uses a screw mechanism, there is a tendency for the tightening mechanism to rotate in the loosening direction due to engagement between a female screw and male screw when rotating the adjustment lever to a position for allowing adjustment of the position of the steering wheel. As a result, the force required for rotating the adjustment lever becomes excessively light, and there is a possibility that the driver who operates the adjustment lever will feel discomfort.